Temperature control device with automatically adjustable backlighting

ABSTRACT

A temperature control device (e.g., a thermostat) may be configured to control an internal heat-generating electrical load so as to accurately measure a present temperature in a space around the temperature control device. The temperature control device may comprise a temperature sensing circuit configured to generate a temperature control signal indicating the present temperature in the space, and a control circuit configured to receive the temperature control signal and to control the internal electrical load. The control circuit may be configured to energize the internal electrical load in an awake state and to cause the internal electrical load to consume less power in an idle state. The control circuit may be configured to control the internal electrical load to a first energy level (e.g., a first intensity) during the awake state and to a second energy level (e.g., second intensity) that is less than the first during the idle state.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/165,091, filed on May 26, 2016, which claims the benefit ofProvisional U.S. Patent Application No. 62/166,230, filed May 26, 2015,the disclosure of which is incorporated herein by reference in itsentirety.

BACKGROUND

Home automation systems, which have become increasing popular, may beused by homeowners to integrate and control multiple electrical and/orelectronic devices in their house. For example, a homeowner may connectappliances, lights, blinds, thermostats, cable or satellite boxes,security systems, telecommunication systems, and the like to each othervia a wireless network. The homeowner may control these devices using acontroller, a remote control device (e.g., such as a wall-mountedkeypad), a user interface provided via a phone, a tablet, a computer,and/or the like, directly connected to the network or remotely connectedvia the Internet. These devices may communicate with each other and thecontroller to, for example, improve their efficiency, their convenience,and/or their usability.

However, some of these devices may interact with one another indetrimental ways. For example, a thermostat may include a displayscreen, and the display screen may give off heat when it is operating.The heat given off by the display screen may throw off the measurementsprovided by the thermostat, such that the thermostat is unable todetermine the true temperature in the space, and as such, is unable toproperly control the temperature of the space. Moreover, the displayscreen may operate in a multitude of varying intensities that may eachgive off a differing amount of heat, further complicating this problem.As such, there is a need for a temperature control device that isconfigured to automatically adjust its temperature readings tocompensate for the heat given off by other internal components, whichfor example, may operate in more than one mode.

SUMMARY

The present disclosure relates to a load control system for controllingthe amount of power delivered to an electrical load, such as a lightingload, and more particularly, to a temperature control device forcontrolling a heating, ventilation, and air conditioning (HVAC) system.

As described herein, a temperature control device may be configured tocontrol an internal heat-generating electrical load so as to accuratelymeasure a present temperature in a space around the temperature controldevice. The temperature control device may comprise a temperaturesensing circuit configured to generate a temperature control signalindicating the present temperature in the space, and a control circuitconfigured to receive the temperature control signal and to control theinternal electrical load. The control circuit may be configured toenergize the electrical load (which causes the electrical load togenerate heat) in an awake state and to cause the electrical load toconsume less power in an idle state so as to generate less heat. When inthe idle state, the control circuit may be configured to periodicallysample the temperature control signal to determine a sampled temperatureand store the sampled temperature in memory. When in the awake state,the control circuit may be further configured to cease sampling thetemperature control signal.

The internal electrical load may be, for example, a button backlightcircuit configured to illuminate a button of the temperature controldevice. The control circuit may be configured to operate in the awakestate in response to an actuation of the button (e.g., the controlcircuit may transition from the idle state to the awake state inresponse to the actuation of the button). The control circuit may beconfigured to control the button backlight circuit to a first intensityduring the awake state and to a second intensity that is less than thefirst intensity during the idle state.

In addition, the temperature control device may comprise a lightdetector circuit configured to measure an ambient light level around thecontrol device. The control circuit may be configured to adjust thefirst intensity of the button backlight circuit during the active statein response to the measured ambient light level and/or adjust the secondintensity of the button backlight circuit during the idle state inresponse to the measured ambient light level. The control circuit may beconfigured to turn the button backlight circuit off when the measuredambient light level exceeds an ambient light threshold during the idlestate.

Although described generally in association with controlling atemperature, it will be appreciated that the temperature control devicedisclosed herein may be configured to measure and/or control otherparameters of the environment including, for example, a relativehumidity (RH) level in the space around the temperature control device.Accordingly, features and functionalities described in the context ofmeasuring and/or controlling a temperature may be applicable to themeasurement and/or control of one or more other parameters (e.g.,relative humidity) as well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example temperature control device(e.g., a wall-mounted thermostat).

FIG. 2 is a block diagram of an example temperature control device.

FIG. 3 illustrates example adjustment curves for adjusting a duty cycleof a current conducted through light-emitting diodes illuminatingbuttons of a temperature control device in response to a measuredambient light level.

FIG. 4 is a flowchart of an example button procedure.

FIG. 5 is a flowchart of an example timer procedure.

FIG. 6 is a flowchart of an example temperature control procedure.

FIG. 7 is a flowchart of an example temperature measurement procedure.

FIG. 8 is a flowchart of an example ambient light detection procedure.

DETAILED DESCRIPTION

FIG. 1 is a perspective view of an example temperature control device(e.g., a wall-mounted thermostat 100) for controlling a heating,ventilation, and air conditioning (HVAC) system. The thermostat 100 maybe configured to control the HVAC system to adjust a present temperatureT_(PRES) in a space in which the thermostat is installed towards asetpoint temperature T_(SET). The thermostat 100 may comprise aninternal temperature sensor (not shown) for measuring the presenttemperature T_(PRES) in the space. Alternatively, the HVAC system couldsimply comprise a heating system or a cooling system.

The thermostat 100 may be configured to communicate (e.g., transmitand/or receive) digital messages with one or more external controldevices via a communication link. The communication link may comprise awired communication link or a wireless communication link, such as aradio-frequency (RF) communication link. The thermostat 100 may beconfigured to adjust the setpoint temperature T_(SET) in response toreceived digital messages. In addition, the thermostat 100 may beconfigured to transmit the present temperature T_(PRES) and/or thesetpoint temperature T_(SET) via one or more digital messages. Thethermostat 100 may be coupled to the HVAC system via a digitalcommunication link, such as an Ethernet link, a BACnet® link, or aModbus link. The HVAC system may comprise, for example, a buildingmanagement system (BMS). Alternatively or additionally, thecommunication link could comprise a traditional analog control link forsimply turning the HVAC system on and off. Examples of load controlsystems having temperature control devices, such as the thermostat 100,are described in greater detail in commonly-assigned U.S. PatentApplication Publication No. 2012/0091213, published Apr. 19, 2012,entitled WALL-MOUNTABLE TEMPERATURE CONTROL DEVICE FOR A LOAD CONTROLSYSTEM HAVING AN ENERGY SAVINGS MODE, and U.S. Patent ApplicationPublication No. 2014/0001977, published Jan. 2, 2014, entitled LOADCONTROL SYSTEM HAVING INDEPENDENTLY-CONTROLLED UNITS RESPONSIVE TO ABROADCAST CONTROLLER, the entire disclosures of which are herebyincorporated by reference.

The thermostat 100 may be configured to control the HVAC system inresponse to occupancy and/or vacancy conditions in the space around(e.g., in the vicinity of) the thermostat 100. The load control device100 may comprise an internal detector, e.g., a pyroelectric infrared(PIR) detector, for receiving infrared energy from an occupant in thespace via a lens 120 to sense the occupancy or vacancy condition in thespace. Alternatively or additionally, the internal detector couldcomprise an ultrasonic detector, a microwave detector, or anycombination of PIR detectors, ultrasonic detectors, and microwavedetectors. The thermostat 100 may be configured to turn the HVAC systemon in response to detecting an occupancy condition in the space and toturn the HVAC system off in response to detecting a vacancy condition inthe space. An example of a wall-mounted control device configured tocontrol an electrical load in response to detecting occupancy andvacancy conditions in described in greater detail in commonly-assignedU.S. Patent Application Publication No. 2012/0313535, published Dec. 13,2012, entitled METHOD AND APPARATUS FOR ADJUSTING AN AMBIENT LIGHTTHRESHOLD, the entire disclosure of which is hereby incorporated byreference.

The thermostat 100 may comprise a visual display 110 for displaying thepresent temperature T_(PRES) and/or the setpoint temperature T_(SET). Inaddition, the visual display 110 may display a mode of the HVAC system(e.g., heating or cooling) and/or a status of a fan of the HVAC system(e.g., on or off, speed, etc.). The visual display 110 may comprise, forexample, a liquid crystal display (LCD) screen or a light-emitting diode(LED) screen. The visual display 110 may be backlight by one or morelights sources (e.g., white backlight LEDs). The thermostat 100 maycomprise a power button 112 for turning on and off the HVAC system. Thethermostat 100 may comprise a fan button 114 for turning on and off thefan (e.g., and for adjusting the speed of the fan) of the HVAC system.The thermostat 100 may also comprise a units-adjust button 115 foradjusting the units in which the present temperature T_(PRES) and/or thesetpoint temperature T_(SET) are displayed on the visual display 110(e.g., Celsius or Fahrenheit). The thermostat 100 may comprise a raisebutton 116 and a lower button 118 for respectively raising and loweringthe setpoint temperature T_(SET) of the thermostat. The thermostat 100may also be configured to adjust the setpoint temperature T_(SET) inresponse to the present time of day according to a predeterminedtimeclock schedule.

One or more of the buttons 112-118 may comprise indicia, such as text oricons, indicating the specific function of the button. The buttons112-118 may be backlit to allow the indicia to be read in a wide rangeof ambient light levels. Each button 112-118 may be made of atranslucent (e.g., transparent, clear, and/or diffusive) material, suchas plastic. The buttons 112-118 may be illuminated by one or more lightsources (e.g., LEDs) located behind each button (e.g., inside of thethermostat 100). In addition, the buttons 112-118 may each have ametallic surface. Specifically, each button 112-118 may have atranslucent body (not shown) and an opaque material, e.g., a metallicsheet (not shown), adhered to a front surface of the body. The indiciamay be etched into the metallic sheet of each button. The illuminationfrom the LEDs may shine through the translucent body, but not throughthe metallic sheet, such that the indicium of each button (that isetched away from the metallic sheet) is illuminated.

When the thermostat 100 is presently being used (e.g., a user ispresently actuating one or more of the buttons 112-118), the thermostatmay operate in an awake state in which the visual display 110 may beturned on and backlit and the buttons 112-118 may each be illuminated toan awake surface illumination intensity L_(SUR1) (e.g., a bright level).When the thermostat 100 is not being used (e.g., the buttons 112-118 arenot presently being actuated), the thermostat may operate in an idlestate in which the backlight for the visual display 110 may be dimmedand the buttons 112-118 may each be illuminated to an idle surfaceillumination intensity L_(SUR2) (e.g., a dim level). The thermostat 100may be configured to wait for an amount of time after the last buttonpress (e.g., approximately 10 seconds) before dimming the backlight forthe visual display 110 and the LEDs behind the buttons 112-118. The idlesurface illumination intensity L_(SUR2) may be less than the awakesurface illumination intensity L_(SUR1) to provide energy savings in theidle state and/or to reduce the heat generated by the backlight LEDs tothus improve the accuracy of the measurements of the present temperatureT_(PRES) by the internal temperature sensor. In addition, the visualdisplay may be turned off and not backlit, and the LEDs behind thebuttons 112-118 may be turned off in the idle state.

The ambient light level in the room in which the thermostat 100 isinstalled may affect a user's ability to read the indicia on the buttons112-118. For example, if the contrast between the brightness of theilluminated indicia and the brightness of the adjacent surface of thebutton is too low, the illuminated indicia may appear washed out to theuser. Accordingly, the thermostat 100 may comprise an ambient lightdetection circuit, which may be configured to measure the ambient lightlevel in the room in which the thermostat is installed. For example, theambient light detection circuit may be located behind the lens 120 andmay receive light through the lens to make a determination of theambient light level in the room. Alternatively, the thermostat 100 maycomprise an opening (not shown) through which the ambient lightdetection circuit may receive light. The thermostat 100 may alsocomprise a light pipe for directing light from outside of the keypad tothe ambient light detection circuit.

The thermostat 100 may be configured to adjust the awake and idlesurface illumination intensities L_(SUR1), L_(SUR2) in response to themeasured ambient light level. For example, the thermostat 100 may beconfigured to increase the awake and idle surface illuminationintensities L_(SUR1), L_(SUR2) if the ambient light level increases anddecrease the awake and idle surface illumination intensities L_(SUR1),L_(SUR2) if the ambient light level decreases.

FIG. 2 is a block diagram of an example temperature control device 200that may be deployed as, for example, the thermostat 100 shown inFIG. 1. The temperature control device 200 may comprise a controlcircuit 210, which may include one or more of a processor (e.g., amicroprocessor), a microcontroller, a programmable logic device (PLD), afield programmable gate array (FPGA), an application specific integratedcircuit (ASIC), or any suitable processing device. The temperaturecontrol device 200 may comprise one or more actuators 212 (e.g.,mechanical tactile switches), which may be actuated in response toactuations of the buttons 112-118. The control circuit 210 may becoupled to the actuators 212 for receiving user inputs.

The temperature control device 200 may comprise a button backlightcircuit 214 for illuminating indicia on one or more buttons (e.g., thebuttons 112-118 of the thermostat 100). For example, the buttonbacklight circuit 214 may comprise one or more LEDs located behind or tothe side of each of the buttons. The control circuit 210 may beconfigured to control an LED current conducted through the LEDs of thebutton backlight circuit 214 to dim a surface illumination intensity ofeach button, e.g., by pulse-width modulating the LED current andadjusting a duty cycle DC_(LED) of the pulse-width modulated LEDcurrent. The control circuit 210 may be configured to control the buttonbacklight circuit 214 to illuminate the buttons to the awake surfaceillumination intensity L_(SUR1) in the awake state and to the idlesurface illumination intensity L_(SUR2) in the idle state. The awakesurface illumination intensity L_(SUR1) may be brighter than the idlesurface illumination intensity L_(SUR2). To illuminate the buttons tothe awake surface illumination intensity L_(SUR1), the control circuit210 may pulse-width modulate the LED current using a first LED dutycycle DC_(LED1). To illuminate the buttons to the idle surfaceillumination intensity L_(SUR2), the control circuit 210 may pulse-widthmodulate the LED current using a second LED duty cycle DC_(LED2), whichmay be smaller than the first LED duty cycle DC_(LED1).

The temperature control device 200 may include a memory 215communicatively coupled to the control circuit 210. The control circuit210 may be configured to use the memory 215 for the storage and/orretrieval of, for example, a setpoint temperature T_(SET) and/or apresent temperature T_(PRES) in the space in which the temperaturecontrol device 200 is installed, the awake surface illuminationintensity L_(SUR1), and/or to the idle surface illumination intensityL_(SUR2). The memory 215 may be implemented as an external integratedcircuit (IC) or as an internal circuit of the control circuit 210.

The temperature control device 200 may comprise a visual display 216(e.g., the visual display 110) for displaying status information for auser, e.g., the present temperature T_(PRES), the setpoint temperatureT_(SET), a mode of the HVAC system (e.g., heating or cooling), and/or astatus of a fan of the HVAC system (e.g., on/off, and/or speed). Forexample, the control circuit 210 may be configured to update the presenttemperature T_(PRES) displayed on the visual display 216 every 50milliseconds. The temperature control device 200 may also comprise adisplay backlight circuit 218 (e.g., having one or more LEDs) forilluminating the visual display 216. The control circuit 210 may beconfigured to turn the display backlight circuit 218 on and off and/oradjust the intensity of the display backlight circuit.

The temperature control device 200 may comprise an HVAC interfacecircuit 220, which may be coupled to an HVAC system that controls thepresent temperature T_(PRES) in the space. The HVAC interface circuit220 may comprise a digital communication circuit for communicating withthe HVAC system via a digital communication link, such as an Ethernetlink, a BACnet® link, or a Modbus link. Alternatively or additionally,the HVAC interface circuit 220 may comprise an analog HVAC controlcircuit for controlling the HVAC system via a traditional analog controllink, e.g., for simply turning the HVAC system on and off. The controlcircuit 210 may be configured to control the HVAC system to adjust thepresent temperature T_(PRES) in the space towards the setpointtemperature T_(SET).

The temperature control device 200 may comprise a temperature sensingcircuit 222 for measuring the present temperature T_(PRES) in the spacein which the temperature control device 200 is installed. Thetemperature sensing circuit 222 may comprise a temperature sensorintegrated circuit, for example, from the Si70xx family of temperaturesensors manufactured by Silicon Labs. The temperature control device 200may generate a temperature control signal V_(TEMP), which may indicatethe measured temperature. The control circuit 210 may be configured toreceive the temperature control signal V_(TEMP) and may store thepresent temperature T_(PRES) in the memory 215. For example, the controlcircuit 210 may be configured to periodically sample the temperaturecontrol signal V_(TEMP) and store the temperature sample in the memory215 (e.g., every second). The control circuit 210 may be configured toaverage a predetermined number of temperature samples (e.g., theprevious 16 temperature samples) stored in the memory 215 to determinethe present temperature T_(PRES), which may also be stored in the memory215. The control circuit 210 may be configured to compare the presenttemperature T_(PRES) to the setpoint temperature T_(SET) and to controlthe HVAC system to adjust the present temperature T_(PRES) in the spacetowards the setpoint temperature T_(SET) if the present temperatureT_(PRES) is outside of a setpoint temperature range around the setpointtemperature T_(SET) (e.g., +/−1° F.).

The temperature control device 200 may also comprise an occupancydetection circuit 224 for detecting an occupancy or vacancy condition inthe vicinity of the load control device. The occupancy detection circuit224 may comprise a detector, e.g., a pyroelectric infrared (PIR)detector, an ultrasonic detector, and/or a microwave detector, fordetecting an occupancy or vacancy condition in the space. For example, aPIR detector may be operable to receive infrared energy from an occupantin the space around the temperature control device 200 through a lens(e.g., the lens 120 shown in FIG. 1) to thus sense the occupancycondition in the space. The control circuit 210 may be configured todetermine a vacancy condition in the space after a timeout periodexpires since the last occupancy condition was detected. The controlcircuit 210 may be configured to turn the HVAC system on and off inresponse to the occupancy detection circuit 224 detecting occupancyand/or vacancy conditions.

The temperature control device 200 may further comprise a communicationcircuit 226, such as, a wired communication circuit or a wirelesscommunication circuit (e.g., an RF transmitter coupled to an antenna fortransmitting RF signals). The control circuit 210 may be coupled to thecommunication circuit 214 and may be configured to adjust the setpointtemperature T_(SET) in response to received digital messages. Thecontrol circuit 210 may also be configured to transmit the presenttemperature T_(PRES) and/or the setpoint temperature T_(SET) via thedigital messages. Alternatively, the communication circuit 226 mayinclude an RF receiver for receiving RF signals, an RF transmitter fortransmitting RF signals, an RF transceiver for transmitting andreceiving RF signals, and/or an infrared (IR) transmitter fortransmitter IR signals.

The temperature control device 200 may comprise a power supply 228 forgenerating a direct-current (DC) supply voltage V_(CC) for powering thecontrol circuit 210 and the other low-voltage circuitry of thetemperature control device. The power supply 228 may be coupled to analternating-current (AC) power source or an external DC power source viaelectrical connections 229. Alternatively or additionally, thetemperature control device 200 may comprise an internal power source(e.g., one or more batteries) in place of or for supplying power to thepower supply 228.

The temperature control device 200 may further comprise an ambient lightdetector 230 (e.g., an ambient light detection circuit) for measuring anambient light level LAMB in the room in which the temperature controldevice 200 is installed. The ambient light detector 230 may generate anambient light detect signal V_(AMB), which may indicate the ambientlight level LAMB and may be received by the control circuit 210. Thecontrol circuit 210 may be configured to adjust the awake and idlesurface illumination intensities L_(SUR1), L_(SUR2) in response to themeasured ambient light level LAMB as determined from ambient lightdetect signal V_(AMB). For example, the control circuit 210 may beconfigured to increase the awake and idle surface illuminationintensities L_(SUR1), L_(SUR2) if the ambient light level increases. Thecontrol circuit 210 may be configured to decrease the awake and idlesurface illumination intensities L_(SUR1), L_(SUR2) if the ambient lightlevel decreases.

The control circuit 210 may be configured to adjust the awake and idlesurface illumination intensities L_(SUR1), L_(SUR2) by adjusting theduty cycle DC_(LED) through each of the LED behind the respectivebuttons. For example, the control circuit 210 may be configured toadjust the first duty cycle DC_(LED1) of the LED current conductedthrough the LEDs of the button backlight circuit 214 in response to themeasured ambient light level LAMB according an awake LED adjustmentcurve DC_(AWAKE), and to adjust the second duty cycle DC_(LED2) of theLED current conducted through the LEDs of the button backlight circuit214 in response to the measured ambient light level LAMB according anidle LED adjustment curve DC_(IDLE). FIG. 3 illustrates example awakeand idle adjustment curves DC_(AWAKE), DC_(IDLE) for adjusting the dutycycle of the LED current of the button backlight circuit 214 in responseto the measured ambient light level LAMB. The awake LED adjustment curveDC_(AWAKE) and the idle LED adjustment curve DC_(IDLE) may be stored inthe memory 215.

The heat generated by the LEDs of the button backlight circuit 214 mayaffect the temperature readings measured by the temperature sensingcircuit 222, such that the temperature control signal V_(TEMP) may notindicate the actual present temperature T_(PRES) in the space. Inaddition, the heat generated by the visual display 216 and LEDs of thedisplay backlight circuit 218 may also affect the temperature readingsmeasured by the temperature sensing circuit 222. For example, since theawake surface illumination intensity L_(SUR1) and the intensity of thedisplay backlight circuit may be greater when the temperature controldevice 200 is in the active state as compared to the inactive state, thetemperature control signal V_(TEMP) may further deviate from the actualpresent temperature T_(PRES) in the space when the temperature controldevice 200 is in the active state. For example, the heat generated bythe button backlight circuit 214, the visual display 216, and thedisplay backlight circuit 218 may cause the temperature inside of thetemperature control device to be approximately 5° F. greater than theactual present temperature T_(PRES) in the space when the temperaturecontrol device 200 is in the active state.

Accordingly, the control circuit 210 may be configured to ceaseperiodically sampling the temperature control signal V_(TEMP) andstoring the present temperature T_(PRES) in the memory 215 in the awakestate. The control circuit 210 may be configured to use the last sampledtemperature stored in the memory 215 as the present temperature T_(PRES)during the awake state, where for example, the last sampled temperaturestored in the memory 215 may have been sampled during the immediatelypreceding idle state. During the awake state, the control circuit 210may be configured to display the present temperature T_(PRES) on thevisual display 216. The control circuit 210 may also be configured tocompare the present temperature T_(PRES) to the setpoint temperatureT_(SET) and may be configured to control the HVAC system if the presenttemperature T_(PRES) is outside of the setpoint temperature range in theawake state (e.g., if the setpoint temperature T_(SET) is adjusted whilein the awake state).

The control circuit 210 may be further configured to wait for an idletime period T_(IDLE-WAIT) after the last button press before changingfrom the awake state to the idle state. Once in the idle state, thecontrol circuit 210 may once again sample the temperature control signalV_(TEMP) to determine the present temperature T_(PRES). For example, theidle time period T_(IDLE-WAIT) may be long enough to allow thetemperature inside of the temperature control device 200 to decrease toan idle steady state temperature that does not significantly affect thetemperature readings measured by the temperature sensing circuit 222.The idle time period T_(IDLE-WAIT) may be a predetermined amount of time(e.g., approximately 180 seconds) stored in the memory 215.Alternatively, the idle time period T_(IDLE-WAIT) may be a function ofthe first duty cycle DC_(LED1) used during the awake state (e.g., asdetermined from the awake adjustment curve DC_(AWAKE) shown in FIG. 3).

When operating in the idle state, the control circuit 210 may beconfigured to control the button backlight circuit 214 to ensure thatthe heat generated by the LEDs of the button backlight circuit may notgreatly affect the temperature readings measured by the temperaturesensing circuit 222. For example, the control circuit 210 may limit theintensity to which each of the LEDs of the button backlight circuit 214are controlled during the idle state. In addition, as shown in FIG. 3,the control circuit 210 may turn off the LEDs of the button backlightcircuit 214 when the ambient light level LAMB exceeds an ambient lightthreshold L_(TH) (e.g., approximately 200 Lux) above which the indiciaon the buttons may be easily distinguished by as user.

The temperature control device 200 may be configured to measure and/orcontrol other parameters of the space around the temperature controldevice. For example, the temperature control device may comprise ahumidity sensing circuit (e.g., including a humidity sensing integratedcircuit) that may be configured to measure a relative humidity level ofthe surround space. The temperature control device 200 may be configuredto adjust the relative humidity level based on the measurement. Thehumidity sensing circuit may be configured to measure the presenttemperature T_(PRES) in the space and use the present temperatureT_(PRES) to determine the relative humidity in the space. The heatgenerated by the LEDs of the button backlight circuit 214, the visualdisplay 216, and/or the LEDs of the display backlight circuit 218 mayaffect the relative humidity readings output by the humidity sensingcircuit. In addition, the temperature sensing circuit 222 may beconfigured as a temperature and humidity sensing circuit. Accordingly,the techniques described herein for mitigating the impact of the heat(and thus the deviation of the readings from the actual parameters) maybe applied to the measurement and/or control of the relative humiditylevel. For example, a last sampled relative humidity level (e.g.,sampled during the immediately preceding idle state) may be stored inthe memory 215 and used during the awake state.

FIGS. 4-8 are simplified flowcharts of example procedures that may beexecuted by a control circuit of a temperature control device (e.g., acontrol circuit of the thermostat 100 of FIG. 1 and/or the controlcircuit 210 of the temperature control device of FIG. 2) to control anHVAC system and adjust the intensity of one or more backlit buttons ofthe temperature control device. FIG. 4 is a flowchart of an examplebutton procedure 400 that may be executed by the control circuit inresponse to an actuation of a button (e.g., one of the buttons 112-118).FIG. 5 is a flowchart of an example timer procedure 500 that may beexecuted by the control circuit when a timer expires, e.g., after anamount of time since a button was last pressed. FIG. 6 is a flowchart ofa temperature control procedure 600 that may be executed periodically bythe control circuit to control the HVAC system. FIG. 7 is a flowchart ofan example temperature measurement procedure 700 that may be executedperiodically by the control circuit in order to measure and store inmemory a present temperature T_(PRES) in a space around the temperaturecontrol device. FIG. 8 is a flowchart of an example ambient lightdetection procedure 800 that may be executed periodically by the controlcircuit in order to measure an ambient light level LAMB in the spacearound the temperature control device and control a backlight circuitfor the backlit buttons (e.g., the button backlight circuit 214). Duringthe procedures 400, 500, 600, 700, 800 of FIGS. 4-8, the control circuitmay use an IDLE flag to keep track of whether the temperature controldevice is operating in an idle state during which the temperaturecontrol device is not being used (e.g., buttons are not being actuated),or in an awake state during which the temperature control device ispresently being used.

Referring to procedure 400, after detecting a button press at 410, thecontrol circuit may clear the IDLE flag at 412 to indicate thetemperature control device is operating in the awake state. At 414, thecontrol circuit may set the present temperature T_(PRES) equal to thelast temperature sample stored in memory. At 416, the control circuitmay increase the amount of power consumed by one or more electricalloads of the temperature control device, such as a visual display (e.g.,the visual display 110, 216), a backlight circuit for the visual display(e.g., the display backlight circuit 218) and/or a backlight circuit forthe backlit buttons (e.g., the button backlight circuit 214). Forexample, the control circuit may turn on the visual display and thebacklight circuit for the visual display at 416. In addition, thecontrol circuit may turn on or increase the intensity of the backlightcircuit for the backlit buttons at 416. At 418, the control circuit maydisplay the present temperature T_(PRES) on the visual display. At 420,the control circuit may process the button press (e.g., the button pressreceived at 410). For example, if a setpoint adjustment button (e.g.,the raise button 116 or the lower button 118 of the thermostat 100) wasactuated, the control circuit may adjust the setpoint temperatureT_(SET) appropriately in response to the actuation. At 422, the controlcircuit may determine whether more than one button was pressed at 410.If so, when the button procedure 400 may loop around to process theadditional button press at 420.

If the control circuit determines that no more buttons have beenactuated at 422, the control circuit may start (or restart) an idletimer at 424. For example, the control circuit may initialize the idletimer with an idle time period T_(IDLE-WAIT) and may start the idletimer decreasing with respect to time at 424. The control circuit mayrecall the value of the idle time period T_(IDLE-WAIT) from memory at424. Alternatively, the control circuit may determine the value of theidle time period T_(IDLE-WAIT) as a function of the present intensity ofthe backlight circuit for the backlit buttons. At 426, the controlcircuit may reduce the amount of power consumed by the electrical loadsof the temperature control device (e.g., the visual display, thebacklight circuit for the visual display, and/or the backlight circuitfor the backlit buttons). For example, the control circuit may turn offthe visual display and the backlight circuit for the visual display at426. In addition, the control circuit may turn off or decrease theintensity of the backlight circuit for the backlit buttons at 426. Forexample, the control circuit may wait for another button press for apredetermined amount of time (e.g., ten seconds) at 422 before reducingthe amount of power consumed by the electrical loads of the temperaturecontrol device at 426. After reducing the amount of power consumed bythe electrical loads of the temperature control device at 426, thebutton procedure 400 may exit.

When the idle timer expires (e.g., the idle timer started at 424 ofprocedure 400), the control circuit may execute the timer procedure 500as shown in FIG. 5. Specifically, after the idle timer expires at 510,the control circuit may set the IDLE flag at step 512, before the timerprocedure 500 exits.

Referring to FIG. 6, the control circuit may execute the temperaturecontrol procedure 600 periodically (e.g., every second) to adjust thepresent temperature T_(PRES) towards the setpoint temperature T_(SET).At 610, the control circuit may compare the present temperature T_(PRES)to the setpoint temperature T_(SET). The control circuit may determinewhether the present temperature T_(PRES) is within a setpointtemperature range around the setpoint temperature T_(SET) (e.g., +/−1°F.) at 612. If the present temperature T_(PRES) is within a setpointtemperature range around the setpoint temperature T_(SET) at 612, thecontrol circuit may not control the HVAC system before the temperaturecontrol procedure 600 exits. However, if the present temperatureT_(PRES) is outside of the setpoint temperature range around thesetpoint temperature T_(SET) at 612, the control circuit may control theHVAC system appropriately so as to adjust the present temperatureT_(PRES) towards the setpoint temperature T_(SET) at 614. Aftercontrolling the HVAC system appropriately, the temperature controlprocedure 600 exits.

Referring to FIG. 7, the control circuit may execute the temperaturemeasurement procedure 700 periodically (e.g., every second) to measureand store the present temperature T_(PRES) in the space around thetemperature control device. The control circuit may determine whetherthe IDLE flag is set at 710 (e.g., whether the temperature controldevice is operating in the idle state). If the IDLE flag is set at 710,the control circuit may sample the temperature control signal V_(TEMP)at 712 and determine the present temperature T_(PRES) from thetemperature control signal V_(TEMP) at 714. The control circuit may thenstore the present temperature T_(PRES) in memory at 716, before thetemperature measurement procedure 700 exits. If the IDLE flag is not setat 710 (e.g., the temperature control device is operating or was justoperating in the awake state), the temperature measurement procedure 700exits. If the IDLE flag is not set at 710, then the present temperatureT_(PRES) may be that which was previously measured and stored by thecontrol circuit when the temperature control device was last in idlestate.

Referring to FIG. 8, the control circuit may execute the ambient lightdetection procedure 800 periodically (e.g., every 100 milliseconds) inorder to measure an ambient light level LAMB in the space around thetemperature control device. The control circuit may sample the ambientlight detect signal V_(AMB) at 810, and then determine the measuredambient light level LAMB using the magnitude of the ambient light detectsignal V_(AMB) at 812. At 814, the control circuit may determine whetherthe IDLE flag is set (e.g., whether the temperature control device isoperating or was just operating in the awake state). If the IDLE flag isnot set at 814, the control circuit may determine the first LED dutycycle DC_(LED1) from the awake adjustment curve DC_(AWAKE) (e.g., usingthe awake adjustment curve DC_(AWAKE) shown in FIG. 3) using themeasured ambient light level LAMB at 816. The control circuit may thenpulse-width modulate the LED current conducted through the buttonbacklight circuit using the first LED duty cycle DC_(LED1) at 818.

If the IDLE flag is set at 814 (e.g., the temperature control device isoperating in the idle state), then the control device may determinewhether the measured ambient light level LAMB is less than or equal toan ambient light threshold L_(TH) (e.g., approximately 200 Lux) at 820.If the measured ambient light level LAMB is less than or equal to anambient light threshold L_(TH) at 820, the control circuit may determinethe second LED duty cycle DC_(LED2) from the idle adjustment curveDC_(IDLE) (e.g., using the idle adjustment curve DC_(IDLE) shown in FIG.3) using the measured ambient light level LAMB at 822. The controlcircuit may then pulse-width modulate the LED current conducted throughthe button backlight circuit using the second LED duty cycle DC_(LED2)at 824, before the ambient light detection procedure 800 exits. If themeasured ambient light level LAMB is greater than the ambient lightthreshold L_(TH) at 820, the control circuit may turn off the backlightcircuit at 826, before the ambient light detection procedure 800 exits.

What is claimed is:
 1. A method for controlling an HVAC system by acontrol circuit of a temperature control device, the method comprising:receiving a temperature control signal indicating a temperature in aspace around the temperature control device; receiving a set pointtemperature; controlling, in an idle state, an internal electrical loadto a first state; sampling, in the idle state, the temperature controlsignal; determining, in the idle state, a sampled temperature based onthe temperature control signal; storing, in the idle state, the sampledtemperature in memory; controlling, in an awake state, the internalelectrical load to a second state, wherein the internal electrical loadconsumes more power in the second state than in the first state; ceasingsampling of the temperature control signal, in the awake state;retrieving, in the awake state, the sampled temperature stored in thememory during the idle state; comparing the retrieved sampledtemperature to the set point temperature; and based on comparing theretrieved sampled temperature to the set point temperature, controllingthe HVAC system.
 2. The method of claim 1, further comprising: enteringthe awake state in response to an actuation of a button.
 3. The methodof claim 2, wherein controlling the internal electrical load comprisescontrolling a button backlight circuit configured to illuminate thebutton with a first duty cycle during the awake state and with a secondduty cycle during the idle state, the second duty cycle having adecreased on time percentage compared to the first duty cycle, thedecreased on time percentage of the second duty cycle being greater thanzero percent.
 4. The method of claim 3, further comprising: controllingthe button backlight circuit in response to an ambient light levelaround the temperature control device measured by a light detectorcircuit.
 5. The method of claim 4, further comprising adjusting thesecond duty cycle of the button backlight circuit during the idle statein response to the ambient light level.
 6. The method of claim 4,further comprising turning off the button backlight circuit when theambient light level exceeds an ambient light threshold during the idlestate.
 7. The method of claim 3, further comprising waiting for a periodof time after the actuation of the button before returning to the idlestate.
 8. The method of claim 7, wherein the period of time is apredetermined value stored in memory.
 9. The method of claim 7, whereinthe period of time is a function of the first duty cycle during theawake state.
 10. The method of claim 1, further comprising displaying apresent temperature on a visual display.
 11. The method of claim 1,wherein the internal electrical load comprises a visual display fordisplaying information for a user, further wherein controlling theelectrical load to the first state comprises turning the visual displayoff during the idle state; and wherein controlling the electrical loadto the second state comprises turning the visual display on during theawake state.
 12. The method of claim 1, wherein the internal electricalload comprises a display backlight circuit for a visual display, furtherwherein controlling the electrical load to the first state comprisesturning the display backlight circuit off during the idle state; andwherein controlling the electrical load to the second state comprisesturning the display backlight circuit on during the awake state.
 13. Amethod comprising: sampling a temperature signal, the temperature signalindicating a temperature in a space around a temperature control device;determining, in an idle state, a sampled temperature based on thetemperature signal; storing, in the idle state, the sampled temperaturein memory; controlling, in the idle state, an internal electrical loadto a first state; and controlling, in an awake state, the internalelectrical load to a second state, wherein the internal electrical loadconsumes more power in the second state than in the first state; ceasingsampling of the temperature signal, in the awake state; retrieving, inthe awake state, the sampled temperature stored in the memory during theidle state; comparing the retrieved sampled temperature to a set pointtemperature; and based on comparing the retrieved sampled temperature tothe set point temperature, controlling an HVAC system.
 14. The method ofclaim 13, further comprising transitioning from the idle state to theawake state in response to an actuation of a button; and waiting for aperiod of time after the actuation of the button before returning to theidle state, the period of time being a predetermined value stored inmemory or a function of an intensity during the awake state.
 15. Themethod of claim 13, further comprising: measuring, via a light detectorcircuit, an ambient light level; and controlling a button backlightcircuit in response to the measured ambient light level.
 16. The methodof claim 15, further comprising adjusting an intensity of the buttonbacklight circuit during the idle state in response to the measuredambient light level.
 17. A method comprising: sampling a temperaturesignal, the temperature signal indicating a temperature in a spacearound a temperature control device; determining, in an idle state, asampled temperature based on the temperature signal; storing, in theidle state, the sampled temperature in memory; controlling, in the idlestate, an internal electrical load to a first state; receiving anactuation of a button; in response to receiving the actuation,transitioning from the idle state to an awake state; controlling, in theawake state, the internal electrical load to a second state, wherein theinternal electrical load consumes more power in the second state than inthe first state; ceasing sampling of the temperature signal, in theawake state; retrieving, in the awake state, the sampled temperaturestored in the memory during the idle state; comparing the retrievedsampled temperature to a set point temperature; and based on comparingthe retrieved sampled temperature to the set point temperature,controlling an HVAC system.
 18. The method of claim 17, whereincontrolling, in the idle state, the internal electrical load to a firststate comprises decreasing a duty cycle of a button backlight circuit inresponse to a measured ambient light level.
 19. The method of claim 17,wherein retrieving, in the awake state, the sampled temperature storedin the memory during the idle state comprises retrieving a most recentsampled temperature stored in memory.